The present invention relates to an image drawing method of a graphic display for a numerical controller which draws an image, such as the locus of a tool, on a display screen based on interpreted contents of an NC command program.
In present-day numerical control (NC) equipment it is an important element how easily and surely an NC command program can be produced or checked, in addition to mere control of a machine tool by numerical control techniques.
An image drawing function is a technical solution to this problem, but it is necessary to improve various operating methods and functions according to the actual conditions of its application.
The image drawing function in the NC equipment is utilized mainly for verifying the operating state of an NC command program after editing (creating and correcting) it. This method has the following advantages over a method of verification by actually operating the machine tool.
(1) Even if the NC command program has an error, there is no danger of, for example, a collision between the machine tool and a workpiece, since the former is not in operation.
(2) The verification by the image drawing method is less time-consuming than the method involving the actual operation of the machine tool.
(3) Since machining is possible even in the image drawing process, utilization of the machine tool is efficient.
(4) Since the magnification for image drawing can be selected arbitrarily by changing the image drawing scale, the operating state of the program can easily be verified both in its entirety and in parts.
Incidentally, in order to verify the whole tool locus of such a shape and size as indicated by the curve l in FIG. 3, it is necessary to set a scale A on which the curve l will entirely go in a selected image drawing space on the display screen. In the case of an unknown NC command program, however, since maximum and minimum values of the tool locus on the image drawing axes (the X- and Y-axis in the illustrated example) are unknown, it is difficult to immediately determine the scale A.
In general, the scale for drawing an image is determined by setting the image drawing space (maximum and minimum values on each axis of the space) in accordance with the object of drawing (an NC command program), and the following methods have heretofore been employed therefor.
(1) The operator preinterprets the contents of the NC command program and sets maximum and minimum values of the image drawing space.
(2) At first, the NC equipment is caused by an "automatic start" function to obtain maximum and minimum values of the program concerned, and then an image is drawn using such a scale and center coordinates of the image drawing space that the maximum and minimum values will go in the space.
(3) Provisional maximum and minimum values for the image drawing space are set, on the basis of which an image is drawn. Then the operator gradually approaches optimum set values through use of functions such as "enlargement, reduction", "graphic form shift" and so forth while observing the image being displayed.
However, these methods possess such defects as follows: